Police are also appealing for information about items believed to have been in Miss O'Callaghan's handbag.
Taxi driver Christopher Halliwell, 47, from Swindon, has been charged with 22-year-old Miss O'Callaghan's murder.
Police have said they are "very close" to identifying the whereabouts of Miss O'Callaghan.
Miss O'Callaghan's body was formally identified by Pete Shawe, the partner of her mother Elaine.
BBC: Sian O'Callaghan 'died of head injuries', inquest hears
He was jailed at Bristol Crown Court on 19 October after admitting Miss O'Callaghan's murder.
Christopher Halliwell led police to Becky Godden's body shortly after he confessed to killing Miss O'Callaghan.
At least Miss O'Sullivan's biography is amusing, and takes a pleasantly sceptical view of Hollywood.
Miss O'Sullivan blamed the studio for putting her in musicals although she could not sing.
Miss O'Sullivan's swimming was a gentle breast-stroke, so a double did the nude scene.
Det Supt Steve Fulcher said he was "quite clear" that one of the bodies was Miss O'Callaghan.
Miss O'Hara told her she was "crazy" and "falling back into the same pattern", the court heard.
BBC: Canal murders accused John Sweeney 'cut up girlfriends'
Halliwell also led police to the body of Becky Godden shortly after he confessed to killing Miss O'Callaghan.
Miss O'Callaghan, 22, had not been seen since she left a nightclub in Swindon early on Saturday morning.
Mr Headley added that Miss O'Callaghan's family were coping "as well as you or I would in these situations".
BBC: Police 'very close' to finding missing Sian O'Callaghan
Miss O'Callaghan, 22, was last seen leaving the Suju nightclub in Swindon alone at about 0250 GMT on Saturday.
Miss O'Callaghan, 22, disappeared after leaving the town's Suju nightclub on 19 March following a night out with friends.
Miss O'Hara said former model Ms Halstead had been beaten by Mr Sweeney.
Miss O'Callaghan's family had agreed that the tributes could be moved, she added.
In a statement, Halliwell's wife Lisa also said her thoughts were "constantly" with Miss O'Callaghan and Miss Godden's families.
BBC: Christopher Halliwell's daughter in plea for murder truth
Miss O'Callaghan's family have agreed that the tributes can be moved, she added.
Christopher Halliwell, 47, of Ashbury Avenue, Swindon, is accused of killing Miss O'Callaghan.
Spokesman Dean Mayo said the march was a final goodbye to Miss O'Callaghan.
Miss O'Callaghan's body was found near Uffington, Oxfordshire, following her disappearance after leaving the town's Suju nightclub on 19 March.
Also present at Monday's news conference were Miss O'Callaghan's parents Mick, 51, and Elaine, 48, and younger sister Lora, 19.
Ch Supt Steve Headley said Miss O'Callaghan's family were coping "as well as you or I would in these situations".
Miss O'Callaghan disappeared after leaving the Suju nightclub in Swindon a week last Saturday following a night out with friends.
Miss O'Callaghan was abducted by Halliwell after a night out in Swindon and taken to Savernake Forest where he murdered her.
Miss O'Callaghan, 22, from Swindon, disappeared after leaving the town's Suju nightclub on 19 March following a night out with friends.
BBC: Sian O'Callaghan 'died of head injuries', inquest hears
Also present at the news conference were Miss O'Callaghan's parents Mick, 51, and Elaine, 48, brother Liam, 24, and sister Lora, 19.
Miss O'Hara said she last saw her sister in London in 1987 when she was working as a photographer and make-up artist.
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